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1. 2 kV Al _0.64 Ga _0.36 N-channel high electron mobility transistors with passivation and field plates

   https://doi.org/10.35848/1882-0786/ad9db4  

   Alam, Md Tahmidul; Chen, Jiahao; Stephenson, Kenneth; Mamun, Md Abdullah-Al; Mazumder, Abdullah_Al Mamun; Pasayat, Shubhra S; Khan, Asif; Gupta, Chirag (January 2025, Applied Physics Express)

   Abstract High voltage (∼2 kV) Al_0.64Ga_0.36N-channel high electron mobility transistors were fabricated with an on-resistance of ∼75 Ω. mm (∼21 mΩ. cm²). Two field plates of variable dimensions were utilized to optimize the breakdown voltage. The breakdown voltage reached >3 kV (tool limit) before passivation however it reduced to ∼2 kV after Si₃N₄surface passivation and field plate deposition. The breakdown voltage and on-resistance demonstrated a strong linear correlation in a scattered plot of ∼50 measured transistors. The fabricated transistors were electrically characterized and benchmarked against the state-of-the-art high-voltage (> 1 kV) Al-rich (>40%) AlGaN-channel transistors in breakdown voltage and on-resistance, indicating significant progress. 

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2. Influence of electrical field on the susceptibility of gallium nitride transistors to proton irradiation

   https://doi.org/10.1088/1361-6463/ad3f29  

   Rasel, Md Abu Jafar; Schoell, Ryan; Smyth, Christopher M.; Hattar, Khalid; Harris, C. Thomas; Lu, Tzu-Ming; Haque, Aman; Wolfe, Douglas E.; Ren, Fan; Pearton, Stephen J. (April 2024, Journal of Physics D: Applied Physics)

   Abstract Radiation susceptibility of electronic devices is commonly studied as a function of radiation energetics and device physics. Often overlooked is the presence or magnitude of the electrical field, which we hypothesize to play an influential role in low energy radiation. Accordingly, we present a comprehensive study of low-energy proton irradiation on gallium nitride high electron mobility transistors (HEMTs), turning the transistor ON or OFF during irradiation. Commercially available GaN HEMTs were exposed to 300 keV proton irradiation at fluences varying from 3.76 × 10¹²to 3.76 × 10¹⁴cm², and the electrical performance was evaluated in terms of forward saturation current, transconductance, and threshold voltage. The results demonstrate that the presence of an electrical field makes it more susceptible to proton irradiation. The decrease of 12.4% in forward saturation and 19% in transconductance at the lowest fluence in ON mode suggests that both carrier density and mobility are reduced after irradiation. Additionally, a positive shift in threshold voltage (0.32 V and 0.09 V in ON and OFF mode, respectively) indicates the generation of acceptor-like traps due to proton bombardment. high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy analysis reveal significant defects introduction and atom intermixing near AlGaN/GaN interfaces and within the GaN layer after the highest irradiation dose employed in this study. According toin-situRaman spectroscopy, defects caused by irradiation can lead to a rise in self-heating and a considerable increase in (∼750 times) thermoelastic stress in the GaN layer during device operation. The findings indicate device engineering or electrical biasing protocol must be employed to compensate for radiation-induced defects formed during proton irradiation to improve device durability and reliability. 

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3. Exceptional Repetitive-Short-Circuit Robustness of Vertical GaN Fin-JFET at High Voltage

   https://doi.org/10.1109/ISPSD49238.2022.9813618  

   Zhang, R.; Liu, J.; Li, Q.; Pidaparthi, S.; Edwards, A.; Drowley, C.; Zhang, Y. (May 2022, Exceptional Repetitive-Short-Circuit Robustness of Vertical GaN Fin-JFET at High Voltage)

   The limited short circuit (SC) capability of GaN high-electron-mobility transistors (HEMTs) has become a critical concern for their adoption in many power applications. Recently, breakthrough SC robustness was demonstrated in a 650-V rated vertical GaN Fin-JFET with a short circuit withstanding time of over 30 µs at 400 V bus voltage (V BUS ), showing great potential for automotive powertrain and grid applications. This work presents the first study on the repetitive SC robustness of this GaN Fin-JFET at a V BUS of 400 V and 600 V. The GaN Fin-JFET survived 30,000 cycles of 400 V, 10 µs SC stresses without any degradation in device characteristics. At a 600 V V BUS , it survived over 8,000 cycles of 10 µs SC stresses before an open-circuit failure. This open-circuit failure signature allows the GaN Fin-JFET to retain its avalanche breakdown voltage and is highly desirable for system safety. Besides, an increase in gate leakage was observed during the 600 V repetitive test, which can be used as a precursor to predict device failure. As far as we know, this is the first report of an exceptional repetitive SC robustness in a power transistor at a V BUS close to its rated voltage. 

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4. AlN/AlGaN/AlN quantum well channel HEMTs

   https://doi.org/10.1063/5.0145582  

   Singhal, Jashan; Kim, Eungkyun; Hickman, Austin; Chaudhuri, Reet; Cho, Yongjin; Xing, Huili Grace; Jena, Debdeep (May 2023, Applied Physics Letters)

   We present a compositional dependence study of electrical characteristics of AlxGa1−xN quantum well channel-based AlN/AlGaN/AlN high electron mobility transistors (HEMTs) with x=0.25,0.44, and 0.58. This ultra-wide bandgap heterostructure is a candidate for next-generation radio frequency and power electronics. The use of selectively regrown n-type GaN Ohmic contacts results in contact resistance that increases as the Al content of the channel increases. The DC HEMT device characteristics reveal that the maximum drain current densities progressively reduce from 280 to 30 to 1.7 mA/mm for x=0.25,0.44, and 0.58, respectively. This is accompanied by a simultaneous decrease (in magnitude) in threshold voltage from −5.2 to −4.9 to −2.4 V for the three HEMTs. This systematic experimental study of the effects of Al composition x on the transistor characteristics provides valuable insights for engineering AlGaN channel HEMTs on AlN for extreme electronics at high voltages and high temperatures. 

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5. Vertical GaN Fin JFET: A Power Device with Short Circuit Robustness at Avalanche Breakdown Voltage

   https://doi.org/10.1109/IRPS48227.2022.9764569  

   Zhang, R.; Liu, J.; Li, Q.; Pidaparthi, S.; Edwards, A.; Drowley, C.; Zhang, Y. (March 2022, Vertical GaN Fin JFET: A Power Device with Short Circuit Robustness at Avalanche Breakdown Voltage)

   GaN high-electron-mobility transistors (HEMTs) are known to have no avalanche capability and insufficient short-circuit robustness. Recently, breakthrough avalanche and short-circuit capabilities have been experimentally demonstrated in a vertical GaN fin-channel junction-gate field-effect transistor (Fin-JFET), which shows a good promise for using GaN devices in automotive powertrains and electric grids. In particular, GaN Fin-JFETs demonstrated good short-circuit capability at avalanche breakdown voltage (BV AVA ), with a failure-to-open-circuit (FTO) signature. This work presents a comprehensive device physics-based study of the GaN Fin-JFET under short-circuit conditions, particularly at a bus voltage close to BV AVA . Mixed-mode electrothermal TCAD simulations were performed to understand the carrier dynamics, electric field distributions, and temperature profiles in the Fin-JFET under short-circuit and avalanche conditions. The results provide important physical references to understand the unique robustness of the vertical GaN Fin-JFET under the concurrence of short-circuit and avalanche as well as its desirable FTO signature. 

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